Many types of single-unit surface-charging electrode are known (German B 3 522 881). The prongs of such electrodes are very often electrically decoupled by way of upstream resistances in the generator power-supply circuitry. When several such prongs are aligned along a strip, charges can he applied in high-speed printing machinery several meters wide. The resulting electric-field forces are employed to attach surfaces to metal cylinders or to block out multiple-layer surfaces.
Machinery of this type often handles surfaces of different width. When an electrode charges a blank metal-cylinder surface with a corona current, the surface is altered or destroyed. When the charge occurs between two electrodes, impermissibly high currents will flow where there is no surface.
It is for this reason that on-and-off single-unit surface-charging electrodes (German 2 948 902) were developed. Various widths can be accommodated by switching them on and off by hydraulic or pneumatic fluid conveyed to each electrode over fluid-tight lines.
On-and-off electrodes occupy considerable space even without the associated hydraulic and pneumatic systems, and the overall result is a comparatively bulky high-voltage electrode. Also unacceptable in explosion-hazardous areas are the sparks that accompany switching operations, not to mention the discharge sections, creep currents, etc. that occur even while the electrodes are off.
Varying the operating width with electrode hatches made of an insulating material and sliding back and forth over unit electrodes that do not switch on and off is also known. There is a drawback, however, in that the electrodes' prongs will continue to emit charges, which will seek thoroughfare to a matching countervailing potential.
Finally, turning groups of unit electrodes in a compound surface-charging electrode on and off is also known (German 3 725 142).
A drawback to this approach is that one control line and one line to the high-voltage source is needed for each group of electrodes. Furthermore, automatically controlling the groups is complicated.